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Long-term climate change and periodic environmental extremes threaten food and fuel security1 and global crop productivity2-4. Although molecular and adaptive breeding strategies can buffer the effects of climatic stress and improve crop resilience5, these approaches require sufficient knowledge of the genes that underlie productivity and adaptation6-knowledge that has been limited to a small number of well-studied model systems. Here we present the assembly and annotation of the large and complex genome of the polyploid bioenergy crop switchgrass (Panicum virgatum). Analysis of biomass and survival among 732 resequenced genotypes, which were grown across 10 common gardens that span 1,800 km of latitude, jointly revealed extensive genomic evidence of climate adaptation. Climate-gene-biomass associations were abundant but varied considerably among deeply diverged gene pools. Furthermore, we found that gene flow accelerated climate adaptation during the postglacial colonization of northern habitats through introgression of alleles from a pre-adapted northern gene pool. The polyploid nature of switchgrass also enhanced adaptive potential through the fractionation of gene function, as there was an increased level of heritable genetic diversity on the nondominant subgenome. In addition to investigating patterns of climate adaptation, the genome resources and gene-trait associations developed here provide breeders with the necessary tools to increase switchgrass yield for the sustainable production of bioenergy.

The successful use of alternative water sources on urban landscapes and golf courses will require salinity tolerant turfgrasses. The objectives of this study were to develop a greenhouse screening method using overhead irrigation, determine useful measurements for screening germplasm, and determine whether perennial ryegrass (Lolium perenne L.) genotypes with salinity tolerance can be identified. A greenhouse irrigation chamber system was developed to apply salinity treatments (1 [control], 5, 10, or 15 dS [m.sup.-1]) for 10 wk. Eight genotypes of each of five perennial ryegrass cultivars (Palmer III, Paragon GLR, Applaud, Brightstar SLT, and Nui) were arranged in a combined split plot design with three replications in 100% sand trays. For al genotypes, relative percent green ratings, clipping yields, and root and shoot weights were significantly reduced with each level of increased salinity. Significant differences between perennial ryegrass genotypes were also observed. Relative percent green ratings were highly correlated to clipping yields ([r.sup.2] = 0.95; p < 0.001), shoot weights ([r.sup.2] = 0.89; p < 0.001), and root weights ([r.sup.2] = 0.93; p < 0.001), indicating percent green ratings may be used to predict more intensive measurements. This method is a novel technique utilizing overhead irrigation and should be useful in developing improved turfgrass cultivars with salinity tolerance. doi: 10.2135/cropsci2010.03.0134

Brown patch disease, caused by Rhizoctonia solani Kuhn, is one of the most devastating fungal pathogens that occur on tall fescue [Lolium arundinaceum (Schreb.) Darbysh. = Schedonorus arundinaceus (Schreb.) Dumort]. The development of genetic resistance to brown patch would provide the most effective long term control to this disease; however, the genetic mechanism of brown patch resistance in tall fescue is not known. For this study, a diallel cross involving six parents was conducted to investigate the genetic inheritance characteristics of brown patch resistance in tall fescue. Parents and their progeny were evaluated for brown patch resistance in a field experiment conducted over two years in which the field experiment was inoculated with a single isolate of R. solani. Both general combining ability (GCA) and specific combining ability (SCA) effects were significant; however, the GCA accounted for a greater proportion of the sum of squares. Moderate narrow-sense heritability estimates [0.62 (2007) and 0.57 (2008)] were calculated from mid-parent-progeny regression analysis. Estimates of the minimum number of effective genes ranged from 1.0 to 3.2 depending on the parents used in the crosses. The presence of a major gene for resistance was not detected in the study. These results support the idea that brown patch resistance is quantitatively inherited. doi: 10.2135/cropsci2009.02.0071

Interspecific hybridization is a widely used approach to improve crop species. We are pursuing the possibility of using interspecific hybridization between the turfgrass species colonial bentgrass (Agrostis capillaris L.) and creeping bentgrass (A. stolonifera L.) for the improvement of resistance to the fungal disease dollar spot (Sclerotinia homoeocarpa F.T. Bennett) in creeping bentgrass. From a field evaluation of a backcross population, it appears that introgression of dollar spot resistance from colonial bent-grass to creeping bentgrass is possible. We used the backcross population to generate the first genetic linkage map for colonial bentgrass. The map length was 1156 cM and consisted of 212 amplified fragment length polymorphic markers and 110 gene-based markers. Colonial bentgrass is an allotetraploid species (2n = 4x = 28, [A.sub.1] and [A.sub.2] subgenomes). The map consisted of the expected 14 linkage groups, which could be assigned to either the [A.sub.1] or [A.sub.2] homoeologous subgenomes. Although there were dollar spot resistant individuals in the mapping population, no quantitative trait loci associated with resistance were detected.

Gray leaf spot disease, caused by Pyricularia oryzae Cavara, is an important disease in perennial ryegrass (Lolium perenne L.) turf. Host resistance is an ideal and promising approach to disease control. In this study, two diallel crosses involving six parents and eight parents, respectively, of perennial ryegrass were established to investigate the inheritance of gray leaf spot resistance. Parents and progenies were evaluated for gray leaf spot resistance in growth chamber experiments where they were inoculated with a mixture of five pathogen isolates. A field experiment was conducted on the progenies of one diallel cross. Effects of both general combining ability (GCA) and specific combining ability (SCA) were significant in both growth chamber and field tests. However, the GCA variance accounted for the major portion of the total genotypic variance. Narrow-sense heritability calculated by midparent-offspring regression ranged from 0.57 to 0.76, indicating additive gene effects were the major genetic component in control of gray leaf spot. Estimates of minimum number of genes ranged from 2.1 to 4.4, suggesting resistance to gray leaf spot was controlled by a small number of genes. All the results suggested that a breeding program basing on recurrent selection should be effective to improve the resistance to gray leaf spot in perennial ryegrass., GRAY LEAF SPOT has rapidly become one of the most important diseases of perennial ryegrass (Lolium perenne L.) in United States since its identification (Dernoeden, personal communications, 1986; Landschoot and [...]

The identification and selection of germplasm with improved drought tolerance will play an important role in developing turfs with better performance and persistence during drought stress periods. The objectives of the study were to: (i) determine the feasibility of simultaneously selecting plants with low-shoot-to-high-root ratios and increased root mass in lower sand profiles using flexible tubes under greenhouse conditions, and (ii) determine gain from two cycles of selection for increased root production within the flexible tubes. Seeds from two populations of tall fescue (Festuca arundinacea Schreb.) and perennial ryegrass (Loliumpereane L.) were germinated in 29.5% (-1.4 MPa osmotic potential) and 28.5% (-1.2 MPa osmotic potential) polyethylene glycol (PEG), respectively, for each cycle of selection. The most vigorous seedlings were transferred to flexible root tubes, 63.5 cm long filled with silica sand, to evaluate for deep rant produetion in the greenhouse. Clippings were collected weekly and root weights were determined after approximately 8 to 12 wk of growth in the flexible root tubes. The top 2 to 4% of the populations were selected for the following characteristics: clipping weights at or below the mean of the population and root weights (in the bottom 30 cm) at least 1 SD above the mean of the population for the turf-type tall fescue and perennial ryegrass populations. After two cycles of selection for increased root mass in the lower 30 cm, gain from selection was approximately 41% in a narrow population and 81% in a broad population of tall fescue and 130% in a turf-type and 367% in a forage-type perennial ryegrass. This technique should be very successful in developing turfgrasses with improved rooting characteristics., THE IDENTIFICATION and selection of germplasm with improved drought tolerance will play an important role in developing turfs with better performance and persistence during drought stress periods. Drought avoidance characteristics [...]

Kentucky bluegrass (Poa pratensis L.; KBG) has good turf quality with adequate irrigation, but moderate to low drought resistance. Interspecific hybridization of Kentucky bluegrass with Texas bluegrass (Poa arachnifera Turr.; TBG), a drought resistant grass native to Texas, has been made to transfer genes of drought resistance from TBG to KBG. The objectives of this study were (i) to investigate whether the hybrids have improved drought resistance compared with either TBG or KBG by examining physiological responses to drought stress; and (ii) to determine major physiological factors associated with recuperative ability of those plants from drought stress. Plants were exposed to drought stress by withholding irrigation for 42 d in a greenhouse. The experiment consisted of 29 fourth-generation backcrossed hybrids, one third-generation hybrid (BDF), two KBG parents ('C-74', 'Midnight'), and one TBG parent. The genotypes classified into three cluster groups of drought resistance (high, moderate, and low) based on the responses of relative water content (RWC), electrolyte leakage (EL), and photochemical efficiency (Fv/Fm) to drought stress. The RWC and Fv/Fm declined with drought stress, but were maintained at higher levels in the high resistance group than the other group, while EL increased during drought and was lower in the high resistance group. Texas bluegrass, Midnight KBG, and two hybrids were ranked highest in drought resistance. Other hybrids varied in drought resistance, with more hybrids of BDF x Midnight ranked in the high drought resistance group than the hybrids of BDF x C-74. Among all physiological parameters examined, EL was the most sensitive indicator to drought stress, as demonstrated by its most rapid increase in response to the stress. High Fv/Fm and retaining of green leaves during drought stress contributed to fast recovery from drought stress following rewatering., KENTUCKY BLUEGRASS forms attractive turf when supplied with adequate water (Meyer and Funk, 1989), which is used extensively for lawns, athletic fields, and golf courses (Turgeon, 2002). It has moderate [...]

Dollar spot, incited by Sclerotinia homoeocarpa F.T. Bennett, is one of the most important diseases affecting creeping bentgrass (Agrostis stolonifera L.) golf greens, fairways, and tees. Genetic resistance to dollar spot is a promising control strategy. A study was initiated to: (i) evaluate dollar spot resistance of 265 collections of creeping bentgrass in two locations; (ii) determine bentgrass clone stability of dollar spot resistance; and (iii) evaluate 10 resistant and susceptible clones for disease, turf, and leaf traits. The field experiments were arranged in randomized complete blocks with six and five clonally propagated replicates in each of two locations evaluated across 2 yr in North Brunswick, NJ. Five isolates of S. homoeocarpa were used to inoculate the field experiments. New Jersey fairway collections had the highest percentage of stable dollar spot resistant clones compared with Illinois fairway and New Jersey and New York golf green collections in this particular study. Resistant clones maintained a significantly higher turf density and percentage green turf cover and smaller dollar spot diameter sizes compared with susceptible clones., DOLLAR SPOT is a major disease that affects the performance of creeping bentgrass on golf greens, tees, and fairways. More than 70% of fungicides used on golf courses are used [...]

Gray leaf spot, caused by the fungus Pyricularia grisea (Cooke) Sacc. [teleomorph Maguaporthe grisea (T.T. Herbert) Yaegashi & Udagawa], can be a devastating disease on perennial ryegrass (Lolium perenue L.). The identification and utilization of perennial ryegrass cultivars with improved resistance to gray leaf spot would reduce the need for fungicide applications. The objectives of this study were to: (i) evaluate cultivars, experimental selections, and single-plot progenies of perennial ryegrass for resistance to gray leaf spot, (it) develop populations from selected resistant parents to determine improvements in the next generation, and (iii) determine heritability and the response to selection for gray leaf spot resistance in perennial ryegrass populations. Two perennial ryegrass field experiments consisting of commercial cultivars and experimental selections, were established in 2000 and 2001 at Adelphia, NJ. Susceptibility of germplasm to gray leaf spot was evaluated following ephemeral natural outbreaks of the disease that occurred three to four weeks post seeding. Parents with improved resistance to gray leaf spot were selected based on progeny turf plot evaluations in 2000, inter-pollinated and seeded into turf plots in the 2001 experiment. Most cultivars and selections evaluated in both experiments had greater than 50% gray leaf spot disease. The high broad-sense heritability estimate (0.92) and similar response of progeny compared to selected parents indicated that parent selection based on progeny tests was a good selection method to predict the combining ability of the parents. It also proved successful in improving gray leaf spot resistance in the next generation, which will be important for the development of more disease resistant cultivars., GRAY LEAF SPOT has become a significant pathogen of perennial ryegrass. Pyricularia grisea was first associated with foliar blighting of perennial ryegrass in 1985 (Dernoeden, 1996), but was not confirmed [...]

The dollar spot disease incited by Sclerotinia homoeocarpa F.T. Bennet. is a common and destructive disease of both cool- and warm-season grasses throughout the world. Genetic resistance to dollar spot is an important control strategy; however, the genetic mechanism of dollar spot resistance in turfgrasses is unknown. The first objective of this study was to determine broad-sense heritability and predicted gain from selection of dollar spot resistance in creeping bentgrass (Agrostis stolonifera L.). This was completed through dollar spot disease evaluation of 265 randomly selected creeping bentgrass clones arranged in a randomized complete block design with six and five clonally propagated replicates in each of two locations evaluated over 2 yr. Five isolates of S. homoeocarpa were used to inoculate the field studies and applied at a rate of 1.75 g [m.sup.-2] of prepared inoculum. The second objective was to evaluate inheritance characteristics of dollar spot disease resistance. Major gene calculations, heterosis, maternal effects, chi square analysis of segregation ratios, and number of effective factors were determined through the evaluation of dollar spot disease resistance of progeny from controlled crosses between fixed resistant and susceptible bentgrass clones. These progenies along with parental clones were established in field trials and inoculated with dollar spot. The continuous population distribution of phenotypes for clones and progeny indicated that dollar spot resistance may be quantitatively inherited. Broad-sense heritability estimates (0.56 on a single plant basis and 0.90 on an 11-plant clonal mean basis) indicated replication increased selection efficiency and that improvement in dollar spot resistance in creeping bentgrass should be possible. A minimum of two to five effective factors depending on the cross may be associated with dollar spot resistance., DOLLAR SPOT DISEASE is one of the main disease problems on close-cut creeping bentgrass. More than 70% of fungicides used on golf courses are used for control of dollar spot, [...]

The taxonomic classification of the genus Agrostis is one of the most complicated of the grass genera. Classification based upon morphological and anatomical characters is difficult and complicated by the presence of intermediate forms and the misapplication of names. Determining ploidy levels of new germplasm can assist in species determination and is necessary before initiating breeding or genetics studies. The objectives of this study were to (i) evaluate the use of laser flow cytometry as a quick, reliable tool to determine ploidy level and aid in Agrostis species determination, and (ii) identify morphological characters associated with DNA content or ploidy level. The six Agrostis species evaluated were A. canina L. subsp. canina, A. canina L. subsp. montana (Hartm.) Hartm., A. palustris Huds. [= A. stolonifera var. palustris (Huds.) Farw.], A. tenuis Sibth. (= A. capillaris L.), A. castellana Boiss. & Reut., and A. alba L. Ploidy level was determined by flow cytometry and root tip chromosome counts. Plant height, panicle height, flag leaf length, flag leaf width, and highest internode length of mature field-grown spaced plants were measured. Significant differences in 2C DNA content were found between species (P < 0.01) differing in ploidy level. Flow cytometry was effective in differentiating between diploid, tetraploid, and hexaploid species. Chromosome numbers previously reported and those observed in this study were positively correlated with 2C nuclear DNA content (r = 0.98, P < 0.01). Flag leaf length was the only morphological measurement taken that was significantly positively correlated to DNA content (r = 0.98, P < 0.001). The results of this study indicate that laser flow cytometry is a quick, reliable tool to determine ploidy levels and infer certain species of Agrostis. This technique will aid breeders to quickly and accurately determine ploidy levels of new germplasm collections., THE TAXONOMIC CLASSIFICATION of the genus Agrostis is one of the most complicated of the grass genera. Distinguishing Agrostis species and subspecies was difficult in the past because the species [...]

Rain‐out shelters provide an effective tool to establish controlled water‐stress environments by excluding undesired rain events and have been widely used in the selection and breeding of cool‐season turfgrass for improved drought tolerance. However, the efficiency of recurrent selection using rain‐out shelters has seldomly been investigated. In this study, we documented the selection process of tall fescue in one cycle of recurrent selection, compared the drought tolerance of two consecutive generations and estimated selection gain of tall fescue using rain‐out shelters. Depending on days of drought, relative selection gain ranges from −4.20% to 3.60%, indicating small and unstable improvement from the parental generation. A subsequent analysis of experimental data using Bayesian mixed linear model revealed low narrow‐sense heritability estimations (0.18 for parental generation and 0.08 for progeny generation), providing an explanation for this observation. [ABSTRACT FROM AUTHOR]